The present invention relates to combined hydrocracking and isomerization.
Hydrocracking is a well-known process. Typical conditions for hydrocracking include a pressure of 100 to 10,000 psig, a temperature of 600.degree. to 1000.degree.F., a hydrogen rate of 100 to 10,000 standard cubic feet per barrel of feed and a catalyst such as a Group VIII metal or metal compound and/or a Group VIB metal or metal compound on a porous refractory base.
Isomerization of normal paraffins such as n-pentane, n-hexane or n-heptane is widely practiced for production of higher-octane isomers for use in gasoline.
Table I, below, shows the relatively excellent octane values for branched paraffins, i.e., the incentive for isomerization.
TABLE I ______________________________________ Research Octane Motor Octane 3 cc. 3 cc. Hydrocarbon Clear TEL Clear TEL ______________________________________ n-Pentane 62 89 62 84 i-Pentane 92 109 90 105 n-Hexane 25 65 26 65 2-Methylpentane 73 93 74 91 3-Methylpentane 75 93 74 91 2,2-Dimethylbutane 92 106 93 113 (neohexane) 2,3-Dimethylbutane 103 119 94 112 (diisopropyl) ______________________________________
Isomerization processes can be divided into high, low, and ultra-low temperature processes. Rough temperature ranges are: 500.degree.-800.degree.F. for high temperature isomerization; 150.degree.-400.degree.F. for low temperature isomerization; and 31 to 150.degree.F. for ultra-low temperature isomerization.
Patents disclosing low-temperature hydrocarbon isomerization processes include U.S. Pat. No. 3,180,905, which is directed to the use of an aluminum tribromide catalyst, and U.S. Pat. No. 3,227,772, which in general is directed to the use of a metal halide catalyst with hydrogen halide at temperatures in the range of about 50.degree. to 350.degree.F.
Catalysts used for middle to low-temperature range isomerization processes, e.g., 150.degree.-500.degree.F., include platinum on halided alumina wherein the halide content is above 1 weight percent and usually above 2 weight percent. Isomerization processes using these solid high-halide-content catalysts are disclosed, for example, in U.S. Pat. No. 2,999,074 and U.S. Pat. No. 2,927,087. The high halide content can be achieved by subliming a Friedel-Crafts component, such as aluminum chloride, onto the alumina support or treating the alumina support with an organic halide, such as carbon tetrachloride. Such catalysts can be used for isomerization at temperatures of about 300.degree.F. and below.
For typical low-temperature isomerization the catlayst used in AlCl.sub.3 plus hydrogen chloride. Low-temperature isomerization feedstock, dried and preheated to reaction temperature, is combined with a recycle stream (if recycling is practiced), mixed with hydrogen chloride, and passed through a reactor and an aluminum chloride recovery section. Reactor effluent is cooled and flashed to discharge any light gases through a small absorber that recovers hydrogen chloride carried off in the gases. Liquid from the flash drum is stripped to recover hydrogen chloride, and is caustic-washed to remove the last traces of acid. The stripping column is usually operated at a pressure high enough that the stripped hydrogen chloride can be returned directly to the reactor. If recycling of unconverted normal paraffin is practiced, the recycle stream is then fractionated from the product.
Typical reaction conditions are: Catalyst AlCl.sub.3 -HCl Inhibitor H.sub.2 (60 psi) Pressure, psi 300 Temperature, .degree.F. 176-212 Space velocity, V/hr/V 1.0-2.5 HCl conc., wt.% 5 Conversion % 60
Ultra-low temperature isomerization so far has not been employed commercially to a significant extent. Patents which have disclosed ultra-low temperature isomerization process include U.S. Pat. No. 2,956,095, directed to the use of fluosulfonic acid catalysts. U.S. Pat. No. 3,201,494 is directed to ultra-low temperature isomerization using an HF.sup.. antimony pentafluroride catalyst in liquid phase and U.S. Pat. No. 3,394,202 is directed to use of a supported HF.sup.. antimony pentafluoride catalyst. U.S. Pat. No. 3,678,120 discloses the use of a supported HF.sup.. antimony pentafluoride or fluosulfonic acid.sup.. antimony pentafluoride catalyst for low-temperature isomerization much the same as in U.S. Pat. No. 3,394,202.
The prior art does not appear to disclose the combination of hydrocracking-low temperature isomerization of singly branched hexanes, particularly as described in the specific process combinations below.